Double-track Tunnel Research Articles

Model test of foundation pit excavation adjacent to the existing double-lane tunnel

Abstract To study the influence of foundation pit excavation on the adjacent existing double-track tunnel, a model box test with a similarity ratio of 1/50 was carried out. In this paper, the mechanical parameters of loess around the tunnel are determined through laboratory tests, and the miscellaneous fill, loess, sand, tunnel structure, support structure, and retaining wall are prepared by similar principles. The variation of the surface settlement, the deformation of the retaining wall, and the surrounding rock and soil pressure of the tunnel were analyzed by using equipment such as the miniature earth pressure box, dial gauge, and strain gauge. The results of the study showed that the existence of the supporting structure makes the bending moment of the retaining wall show the phenomenon of negative value first, then positive value, and finally negative value. In the process of foundation pit excavation, when the horizontal distance of the model surface is 4 times the excavation depth, the foundation pit excavation has little effect on the settlement of the model surface. The earth pressure value of the surrounding rock decreases with the increase of the excavation depth of the foundation pit. The earth pressure value of the surrounding rock is the right > the left > the lower part > the upper part and the excavation of the foundation pit has the greatest influence on the upper and left sides of the surrounding rock close to the side of the foundation pit, and the least impact on the right side of the surrounding rock.

Investigation of thermodynamic parameters of the air environment in subway lines with single-track and double-track tunnels

Investigation of thermodynamic parameters of the air environment in subway lines with single-track and double-track tunnels

Multi-task Gaussian Processes based transient aerodynamic load reconstruction for maglev vehicle using acceleration response

The accurate estimation of aerodynamic loads is crucial for developing high-speed maglev trains, which can reach speeds of up to 600 km/h. Traditionally, this estimation has been achieved through computational aerodynamic simulation or direct pressure measurement. In this paper, we propose a novel framework for reconstructing transient aerodynamic loads on maglev vehicles using on-board acceleration measurements. In the framework, an inverse mathematical model that correlates the measured acceleration and external aerodynamic loads is derived from a well-calibrated maglev vehicle model. To avoid the ill-posed problem when solving the inverse mathematical model, a multi-task Gaussian Processes method is proposed, in which all reconstructed transient aerodynamic loads are treated as Gaussian Processes and the closed-form posterior distributions of these aerodynamic loads could be calculated. To validate the proposed framework, a set of transient vibration data collected from an operational maglev train passing through a double-track tunnel is utilized for load reconstruction. The results demonstrate that the framework offers a cost-effective and efficient means to obtain aerodynamic loads, highlighting its practical relevance for aerodynamic field testing in the context of evolving high-speed maglev technologies.

Safety assessment of the construction of double track tunnels underneah exsiting railway tunnels

The ground disturbance caused by the tunnel construction will inevitably have an impact on the upper part of the constructed tunnel structure, and the railroad tunnel requires a very high level of control over the structural settlement deformation. For the problem of double-hole tunnel under the built tunnel, this paper takes Chongqing Mingyue Mountain Tunnel under the built Shanghai-Rong Railway Paihua Cave tunnel and Zheng-Yu Railway tunnel as the engineering background, and starts from the mechanism of ground loss caused by tunnel excavation, firstly, the settlement at the height of the existing tunnel strata is obtained through theoretical analysis, and the new Mingyue Mountain Tunnel under the Shanghai-Rong Railway tunnel is determined to be a more dangerous section. Further simulate and calculate the dynamic excavation process of the new double-hole tunnel underpass, and study the settlement deformation law of the Mingyue Mountain Tunnel underpassing the Hurong Railway Tunnel. According to the requirements of railroad tunnel for settlement deformation control, the new tunnel is determined to be constructed by step method to ensure the safety of railroad tunnel. The shortcomings of the theoretical calculation are analyzed to illustrate the important role of numerical simulation in the evaluation of tunnel underpass projects.

Alleviation of micro-pressure waves radiated from tunnel hoods

When a train enters a tunnel, an impulsive pressure wave, called a micro-pressure wave (MPW), radiates from the tunnel exit. The MPW causes infrasound and audible noise near the tunnel portals; therefore, it should be reduced for environmental reasons. A typical countermeasure is the installation of a hood at the tunnel entrance portal. In a previous study, we proposed a new type of hood that combined two hoods with constant and different cross-sectional areas (a two-step hood). The two-step hood was more effective than the existing hoods. However, because the cross-sectional area of the portal of the two-step hood was larger than that of the existing hoods, the MPW radiated by a train entering the opposite tunnel portal increased in a double-track tunnel. This study developed a new concept for a tunnel hood that reduces the radiated MPW (performance at the MPW radiation stage) while maintaining the performance in terms of reducing the maximum pressure gradient of the compression wave (CW) generated by a train entering a tunnel (performance at the CW generation stage). The desired specifications for satisfying both performances were determined through calculations based on acoustic theory, and their performances were investigated through model experiments using a train model launcher. As the results, the desired specifications were lh3/lw>0.6, lh1≈lh2>lwMt/1-Mt, σh1=1.4, and σh2=2.5, where lh1, lh2, and lh3 are lengths of first hood, second hood, and added lateral wall, respectively, lw is wavefront thickness, Mt is the train’s Mach number, and σh1 and σh2 are the cross-sectional area ratio of the first and second hoods to tunnel, respectively. The developed hood is expected to provide more effective performance in mitigating MPW than existing hoods.

Field measurements of aerodynamic pressures induced by suburban rail transit train passing through double-track tunnel with mid-partition wall

ABSTRACT Suburban rail lines, which provide fast connections between city centre and the surrounding suburbs, are attracting more and more attention from cities. As a train passes through the tunnel quickly, it tends to produce significant aerodynamic effects. In this study, a series of field measurement experiments were carried out in two tunnels with the mid-partition wall. The influence of train speed and tunnel length on the aerodynamic pressure was analysed. The aerodynamic pressure in adjacent tunnel was also discussed. Furthermore, the attenuation law and coefficient of aerodynamic pressure in tunnels with mid-partition walls were discussed. On this basis, a theoretical calculation model for predicting the peak positive pressure inside tunnels with different lengths and attenuation characteristics was established. The results show that the tunnel length not only affects the amplitude of the pressure, but also significantly affects the distribution trend of the pressure peak in the longitudinal direction. The propagation and reflection processes of pressure waves also exist in the adjacent tunnel on the other side of the partition, and they are synchronous. For the horse-shaped tunnel with mid-partition walls, the peak pressure inside the tunnel is directly proportional to the 2.05–2.20 power of the train speed, and the peak pressure decays exponentially with time. The pressure attenuation coefficient is greatly influenced by the placement of the measuring point, ranging from 4.957 × 10 − 5 to 8.184 × 10 − 5 depending on the position of the measurement point. This work provides important data support for studying the tunnel aerodynamic effects and verifying related numerical simulations.

Study on Numerical Simulation of Surrounding Rock Structure Safety of Urban Underwater Shield Tunnel: A Case in Chongqing

Based on the engineering background of shield construction of a subway section in Chongqing, which needs to pass through a park and there is a lake inside this park, this paper adopts theoretical analysis methods and numerical simulation calculation methods to explore the distribution law of the seepage field and the characteristics of water pressure in lining segments during shield tunneling. The results show that, during the whole excavation of a double-track tunnel with EPB shield, the maximum vertical effective stress is about 4.24 MPa, which is located at the arch foot of the tunnel. The maximum effective stress in the horizontal direction is about 3.61 MPa, which is located on both side walls of the tunnel in the horizontal direction; after the left and right tunnels are excavated in sequence, a “double precipitation funnel-shaped” pore pressure distribution is formed around the tunnel; during the construction of the shield tunnel, the vertical displacement and horizontal displacement of the surrounding rock show an increasing trend and gradually tend to be stable values of 24.09 mm and 25.28 mm; the segment vault has settlement, the maximum settlement is 21.8 mm, the arch bottom has uplift, and the maximum uplift is 24.4 mm. The maximum horizontal displacement of the segment appears on both sides of the arch waist, and the maximum horizontal displacement decreases with the increase of excavation steps; the positive bending moment of the lining segment is mainly distributed on both sides of the arch crown, and the negative bending moment is mainly distributed on both sides of the arch bottom. The axial force of the lining segment is compressive stress, and the maximum axial force is mainly distributed on both sides of the arch waist. The maximum normal shear stress occurs on both sides of the segment arch bottom. The study conclusions provide theoretical foundation and a new guidance for long-term safety evaluation of underwater tunnel structures.

Enhanced methodology for thermal management area assessment of metro lines

The article analyzes the operation of metro lines with doubletrack and single-track tunnels in the Russian Federation. Simultaneous activation of traffic on single-track and double-track tunnels affects the management of thermal and humidity parameters of the air environment on metro lines. Currently, there is limited experience in using shared lines. The study conducted an analysis of the features in the formation of thermal and ventilation regimes in double-track and single-track subway tunnels. It also examined the temperature regime of the station when mixing air flows from a double-track tunnel between stations and the flow from one of the stations. An algorithm has been defined for controlling the thermal and humidity parameters of the environment in underground structures. Measures are proposed to minimize the consequences of combining air flows and normalize microclimate parameters. The analysis of air mass movement revealed that the air temperature at the station located beyond the junction point of the double-track tunnel section and single-track tunnels is influenced by circulation flows in single-track tunnels, as well as the flow rate and temperature of the air coming from the double-track tunnel.

Methodological approach to determining the area of air recycling on metro lines with double track tunnels

The article discusses the issues of operating existing metro lines with double-track tunnels. Significant differences between average annual, average monthly and extreme values of outdoor air temperature affecting the thermodynamic and thermophysical parameters of the mine atmosphere of subway tunnels, both in Russia and abroad, are analyzed. The results of a comprehensive analysis of the conditions that determine the temperature regime of the lines of double-track tunnels are presented. Air recirculation in the tunnels has been determined considering climatic conditions. Engineering and technical calculations have been carried out in metro tunnels when the seasonal periods of their operation change. Each of these periods is characterized by its own temperature, for example, for the winter period these are: average winter temperatures, temperatures of the coldest month, the coldest five-day period. The obtained results of the research work will make it possible to select the amount of air for each specific variant of the year, which will ensure, during the operation of this kind of metro lines, the standard thermodynamic parameters of the air environment, both in underground stations and in metro tunnels, and possibly lead to a positive economic effect.

Influence of the door opening on the pressure transient caused by the high-speed subway train passing through the double-track tunnel with the mid-partition wall

Double track tunnel with mid-partition wall is a widely used subway tunnel. In such tunnels, in order to avoid the fire door on the middle partition wall from invading the gauge, the fire door is often removed to form door openings. The existence of door opening connects two parallel tunnels, which affects the aerodynamic effect caused by high-speed subway train passing through the tunnel. In this study, a double track tunnel with mid-partition wall was taken as an example to analyze the aerodynamic effect of high-speed subway train under the door opening conditions, moreover, the surface pressure of two adjacent tunnels and train surface pressure was also analyzed. In addition, the propagation mechanism of pressure wave in open door tunnel was analyzed in detail, and the superposition law of branch pressure wave caused by open door was pointed out. The results indicated that the presence of door openings is beneficial for controlling the peak pressure on the tunnel surface and train surface. For a door opening with a cross-sectional area of 5 m2 (cross-sectional area ratio of 0.116), when the door opening is located 300 m and 700 m away from the tunnel entrance, the peak positive pressure can be reduced by up to 21.9 % and the peak negative pressure can be reduced by 21.1 %. The cross-sectional area and number of door openings have a limited effect on reducing the peak pressure of the tunnel. Compared to the number of door openings, the position of the door opening has a more significant impact on the peak pressure inside the tunnel and on the surface of the train.

Prediction for the surface settlement of double-track subway tunnels for shallow buried loess based on peck formula

In the process of constructing double-track subway tunnels in shallow buried loess areas, the interaction of double-track tunnels is significantly influenced by the net distance and the cross-section size, which is challenging to control the surface settlement. Therefore, the surface settlement prediction is essential while constructing double-track subway tunnels in shallow buried loess areas. The paper analyzed the surface settlement law of shallow buried double-track tunnels in loess areas through theoretical research and numerical simulation. The research results show that with the decrease of the net distance, the surface settlement superimposed curve was double V shape -W shape - single V shape. When the superimposed curve is double V shape and W shape, the Peck formula was used to calculate the surface settlement curve of the single-track tunnel, then superimposed to obtain the final surface settlement curve. When the superimposed surface settlement curve was V shape, based on the Peck formula, the formula for predicting the surface settlement suitable for symmetry and asymmetry was established. The net distance ratio and the area ratio were defined, and considering the tunnel’s interaction, the value and position of the maximum were corrected. Then numerical tests were carried out 16 times with different net distance ratios and area ratios, to determine the parameters of increments and position offsets of the maximum regarding the net distance ratio and the area ratio. Finally, two engineering were conducted for verifying the rationality and applicability exhibited by the prediction formula. The prediction formula served for predicting the surface settlement of double-track subway tunnels in shallow buried loess areas. Which can reduce construction risks and assure the safety of buildings above the ground.

Lateral damage mechanism of the double-track tunnel in the mountainous layered soft rock and NPR anchor cable control

Due to complex geological formations, lateral damage often occurs during excavation in mountainous layered soft rock double-track tunnels. This paper discusses the stresses and the damage characteristics of the surrounding rock under overload in a mountainous layered soft rock double-track tunnel through indoor model experiments to provide a basis for the effective control of lateral damage. The experiments show that the conventional support method cannot effectively control the lateral damage due to interlayer sliding. Therefore, the negative Poisson’s ratio (NPR) anchor/cable control method is proposed. And the scientificity and feasibility of the NPR anchor/cable control technology are proved by the field application and monitoring data of the Minxian Tunnel and Changning Tunnel. It is further demonstrated that high preload is the most effective way to control the lateral damage in layered soft rock tunnels.

Analysis of Loose Surrounding Rock Deformation and Slope Stability at Shallow Double-Track Tunnel Portal: A Case Study

A low-clearance tunnel portal in the shallow-buried, joint-developed, broken, and loose surrounding rock slope deposit may cause safety issues during construction. In this study, the Guanyin Mountain Tunnel of the Chong-Ai expressway was taken as a case study, and the characteristics of the loose and broken surrounding rocks, their low clearance, and shallow buried bias were comprehensively studied. The three-dimensional numerical model of the Guanyin Mountain tunnel portal section was constructed by the Rhino, AutoCAD, and FLAC 3D software, and the whole construction process of the tunnel portal was simulated. Under the conditions of loose and broken surrounding rocks, the surrounding rock deformation, surface settlement, and slope stability at the portal of the shallow buried tunnel with a small clear distance during the construction of the center diaphragm (CD) method and circular reserved core soil method were studied. The following conclusions are drawn. During the simulated excavation of the tunnel, the maximum surface settlement is 10.74 mm, which meets the requirement of the specification. When the left tunnel is excavated, the surrounding rock deformation of the right arch shoulder should be carefully considered. The maximum deformation value can reach 14.314 mm. After excavation, the deformation rate of the right tunnel is large, and initial support should be installed in time. Since the stratum rock at the portal of the tunnel is strongly weathered, the uplift value of the arch bottom is large and gradually decreases along the axial direction. The tunnel arch bottom and arch foot are plastic areas prone to tensile damage. Therefore, it is imperative to strengthen the inverted arch support of the tunnel in the strongly weathered rock stratum. The excavation sequence of the tunnel portal section adopts the method of excavating the left tunnel first and then excavating the right tunnel, which is more conducive to ensuring the slope stability.

Testing and Analysis of the Vibration Response Characteristics of Heavy-Haul Railway Tunnels and Surrounding Soil with Base Voids

This paper discusses research on the dynamic response characteristics of a heavy-haul railway tunnel and the surrounding soil under the conditions of substrate health and a base void. The detection results of the base condition of 20 double-track tunnels for a heavy-haul railway show the main distribution law of base voids. Based on this, a 1:20 scale test model of a heavy-haul railway tunnel is established. The vibration load of the train is established by a vibration exciter arranged at the tunnel invert. The dynamic response and attenuation law of a heavy-haul railway tunnel lining structure and the surrounding soil are tested using acceleration sensors, strain gauges, and soil pressure boxes. The research results show that most of the diseases are concentrated below the heavy-haul line. The base void causes the peak acceleration of the nearby tunnel invert to increase by 55.6%. Tunnel annular construction joints reduce the conductivity of the vibration waves in the axial direction of the tunnel. The acceleration attenuation rate of the soil above the tunnel invert is significantly less than that under the invert. The base void reduces the acceleration of the nearby soil layer by 19.4% and increases the stress on the surface of the nearby tunnel invert by 21.3%, and the stress change amplitude increases by 0.55%. The tunnel structure in the area of the base void experiences fatigue damage. The base void causes the compaction and bearing capacity of the nearby soil to decrease and the softening speed of the tunnel basement soil layer to increase. Therefore, for the basement damage to heavy-haul railway tunnels, “early detection, early treatment” should be performed.

Study of unsteady aerodynamic performance of a high-speed train entering a double-track tunnel under crosswind conditions

Significant variation exists in the aerodynamic performances of high-speed trains (HSTs) traveling in different infrastructure scenarios. When high-speed trains travel from one infrastructure scenario to another, the aerodynamic loads acting on the trains change significantly. To investigate the safety as a HST enters a tunnel under crosswind conditions, the unsteady aerodynamic performance of the HST and the flow structures around the train were numerically studied. The results demonstrated that the flow field and the pressure field were symmetrically distributed under conditions with no crosswind, while the distribution of the flow field and the pressure field were clearly asymmetric when crosswinds were present at the tunnel entrance. Furthermore, the flow structures near the train and the pressure distributed on the train surfaces outside the tunnel were most severely affected by the presence of crosswinds. Vortex structures appeared on the windward side surface of the train inside the tunnel and on the leeward side surface of the train outside the tunnel during the entrance of the train into the tunnel. Due to the sudden changes in the flow and the pressure as the train entered the tunnel, the aerodynamic loads changed drastically, and the variations of each vehicle were different, resulting in complex dynamic responses, including lateral vibrations and pitching movement. In particular, the aerodynamic performance of the rear vehicle was the worst as the train entered the tunnel when no crosswind conditions existed, while the head vehicle was the most negatively affected for safe operation of the HST when strong crosswinds were present at the tunnel entrance.

Aerodynamic effect analysis of high-speed train entering and leaving single and double track tunnels under crosswind

ABSTRACT The aerodynamic effects of high-speed train running in and out of single-hole single-track and single-hole double-track tunnels and across bridges and tunnels under crosswind are studied by means of train moving model experiment and numerical simulation. The pressure fluctuation amplitude of the train entering and exiting the single-track tunnel is larger than that of the train entering and exiting the double-track tunnel under the crosswind, and the maximum amplitude can reach 2824 Pa. When the train enters or exits the single-track tunnel, the aerodynamic force of the leading carriage is less than that of the double-track tunnel except the yawing moment. Except for the yawing moment, the aerodynamic force of the tail carriage in single-track is greater than that of the double-track tunnel at the stage of the train leaving the tunnel; when the train enters the single-track tunnel, the aerodynamic force is less than that of the double-track tunnel.

Ground vibrations induced by the passage of double-line trains in underground tunnels

Subway systems consist of double lines to transport passengers in the outbound and inbound directions. The existing prediction models for subway-induced vibrations ignored the superimposed effect caused by the successive passage of double-line trains. This study develops a computationally efficient method to simulate ground vibrations during the simultaneous passage of double-line trains in underground tunnels. An analytical model is applied to calculate the transfer function of a track-tunnel-ground system in a multi-layered half-space. Two alternative designs of tunnels in a double-line subway system are considered, which are a double-track tunnel and twin single-track tunnels. By introducing the relation between two different moving frames of reference, a fully coupled solution for the train-track-tunnel-ground system that considers the dynamic interaction between the double-line trains is proposed. The numerical results indicate that the simultaneous passage of double-line trains induces a significant superimposed effect of ground vibrations. The superimposed effect can increase the vertical velocity in the one-third octave spectrum by up to 5 dB, and the running RMS value by up to 40% under the same track roughness. The ground vibrations from one double-track tunnel are more than 30% higher than those from two single-track tunnels due to the passage of the single-line train and double-line trains.

Unsteady slipstream of a train passing through a high-speed railway tunnel with a cave

Abstract The cave is of great importance for the storage of equipment and to avoid having workers in the tunnel, but it changes the tunnel section, leads to a change of slipstream and affects the safety of trains and workers. The Re-normalization group (RNG) k-ε turbulence method is used to investigate the slipstream induced by a single train passing through a double-track tunnel at 350 km/h. The slipstream in a tunnel with and without a cave is compared. The slipstream components in three directions are reported comprehensively. The results show that the existence of a cave changes the slipstream at the tail of the train. At measurement points before and after the train passes the cave, the intensity of the slipstream at the tail is mitigated; as the train passes the cave, the tail slipstream is enhanced to a certain extent. With increasing lateral distance, the peak value of the slipstream with a cave decreases faster than that without a cave. These findings suggest that the presence of a cave mitigates the slipstream intensity, but special attention should be paid to the design of ancillary facilities, especially their relative location.

Geological information prediction for shield machine using an enhanced multi-head self-attention convolution neural network with two-stage feature extraction

Due to the closed working environment of shield machines, the construction personnel cannot observe the construction geological environment, which seriously restricts the safety and efficiency of the tunneling process. In this study, we present an enhanced multi-head self-attention convolution neural network (EMSACNN) with two-stage feature extraction for geological condition prediction of shield machine. Firstly, we select 30 important parameters according to statistical analysis method and the working principle of the shield machine. Then, we delete the non-working sample data, and combine 10 consecutive data as the input of the model. Thereafter, to deeply mine and extract essential and relevant features, we build a novel model combined with the particularity of the geological type recognition task, in which an enhanced multi-head self-attention block is utilized as the first feature extractor to fully extract the correlation of geological information of adjacent working face of tunnel, and two-dimensional CNN (2dCNN) is utilized as the second feature extractor. The performance and superiority of proposed EMSACNN are verified by the actual data collected by the shield machine used in the construction of a double-track tunnel in Guangzhou, China. The results show that EMSACNN achieves at least 96% accuracy on the test sets of the two tunnels, and all the evaluation indicators of EMSACNN are much better than those of classical AI model and the model that use only the second-stage feature extractor. Therefore, the proposed EMSACNN achieves high accuracy and strong generalization for geological information prediction of shield machine, which is of great guiding significance to engineering practice.

The Change in Dynamic Response Distribution of Double-Track Tunnel Structure Caused by Adding Middle Partition Wall

Adding a middle partition wall is an effective method to prevent the interaction between the upper and lower subway lines in a double-track tunnel, and the subsequent change in the dynamic response of the tunnel structure caused by adding a middle partition wall has drawn attention. We analyzed the displacement and acceleration responses of the upper part (zone A), the lower part (zone B), the tunnel bed and the surrounding connecting part (zone C) of the double-track tunnel by establishing a two-dimensional finite element model of the double-track tunnel and soil with and without a middle partition wall. The numerical results demonstrate that the addition of the middle partition wall improves the displacement and acceleration response distribution of the double-track tunnel structure. Compared with single-train traffic, the addition of the middle partition wall brings more obvious changes to the dynamic response of the double-track tunnel during double-train traffic. The maximum displacement response decreases from 5.881 mm to 5.335 mm, and the maximum acceleration response decreases from 18.51 m/s2 to 16.62 m/s2. The displacement response value in the upper part increases from 1.0 mm to 1.5 mm, the acceleration response value increases from 3.0 m/s2 to 4.6 m/s2, the displacement response value in the tunnel bed and the surrounding connecting part decreases from 5.0 mm to 3.0 mm, and the acceleration response value in the tunnel bed and the surrounding connecting part decreases from 18.0 m/s2 to 10.0 m/s2. There is no obvious change in the lower part. During double-train traffic, after adding the middle partition wall, the horizontal displacement and horizontal acceleration response values of the double-track tunnel structure decrease by about 30% to 45%; the vertical displacement response value of the connection between the middle partition wall and the lining increases from 1.337 mm to 1.774 mm, an increase of 32.7%, and the vertical acceleration of the lower half of the tunnel lining is partially transferred to the upper half. The response values of horizontal displacement and acceleration in the middle part of the middle partition wall are the largest, at 1.6 mm and 6.0 m/s2, while the response values of vertical displacement and acceleration in the bottom of the partition wall are the largest, at 3.3 mm and 9.0 m/s2. The research results provide a reference for the structural design of middle partition walls to ensure the safety and stability of trains running in double-track tunnels.